Electromagnetic flowmeters are commonly used in various industries to measure the flow rate of conductive fluids flowing through pipelines or other conduits. In principle, electromagnetic flowmeters generate a magnetic field in a conduit extending through the meter. When conductive fluid flows through the conduit, the magnetic field induces a voltage difference between two locations in the fluid that are spaced apart in a direction transverse to the fluid flow and the magnetic field. The magnitude of this voltage difference is related to flow rate. Thus, the fluid flow rate can be measured by detecting and determining the amount of the voltage difference. The voltage difference is calibrated to the fluid velocity in the conduit. The fluid velocity can be used in combination with the cross sectional flow area to obtain a volumetric flow rate measurement. If the density of the fluid is known, the volumetric flow rate can be converted to a mass flow rate.
Sometimes the conduit might not be completely filled with fluid. If the fluid level drops below the level of the electrodes used to measure the voltage difference, a magnetic flowmeter cannot provide useful measurements of the fluid flow rate. Some conventional electromagnetic meters include so-called empty pipe detection systems, which typically detect whether or not the electrodes are immersed in the fluid. However, the present inventor has made certain improvements, which will be described in detail below.